1. Field of the Invention
This invention involves an arrangement for smooth and continuous feeding of pressurized abrasive material, in particular, for feeding abrasive powder in abrasive dental devices.
2. Description of the Related Art
A standing goal in dentistry is to find a way to efficiently and precisely reduce a tooth, for example, in preparation for a filling, or to remove plaque, with as little discomfort to the patient as possible. One promising alternative to the conventional rotating or vibrating mechanical drill bit is a tool that directs a fine stream of a pressurized abrasive powder against the surface of the tooth. Experience has indicated that these devices cause much less trauma to the tooth yet are at least as effective at removing tooth enamel as a conventional drill head. Moreover, since there is no hard physical contact between the surface of the tooth and a fast-vibrating or rotating drill bit or head, abrasive systems also reduce the risk of chipping the tooth surface.
The general technique of treating teeth using an abrasive jet is described in the following publications:
"Technic for Nonmechanical Preparation of Cavities and Prophylaxis," Robert Black, Journal of the American Dental Association, Vol. 32, pp. 955-965, 1945;
"Airbrasive: some fundamentals," Robert Black, Journal of the American Dental Association, Vol. 41, pp. 701-710, 1950;
"Airbrasive Technic Discussed," Harold Roach, Journal of the American Dental Association, Vol. 43, p. 108, 1951; and
"Analysis of airbrasive procedures in dental practice," Sidney Epstein, Journal of the American Dental Association, Vol. 43, p. 578, 1951.
Known devices for treating teeth with an abrasive jet include those described in:
U.S. Pat. No. 2,696,049 (Black, Dec. 7, 1954); PA0 U.S. Pat. No. 3,852,918 (Black, Dec. 10, 1974); PA0 U.S. Pat. No. 4,412,402 (Gallant, Nov. 1, 1983); PA0 U.S. Pat. No. 4,522,597 (Gallant, Jun. 11, 1985); PA0 U.S. Pat. No. 4,635,897 (Gallant, Jan. 13, 1987); PA0 U.S. Pat. No. 4,708,534 (Gallant, Nov. 24, 1987); PA0 U.S. Pat. No. 4,733,503 (Gallant, Mar. 29, 1988); PA0 U.S. Pat. No. 4,893,440 (Gallant et al., Jan. 16, 1990); PA0 U.S. Pat. No. 5,275,561 (Goldsmith, Jan. 4, 1994); PA0 U.S. Pat. No. 5,330,354 (Gallant, Jul. 19, 1994); PA0 U.S. Pat. No. 5,334,016 (Goldsmith, Aug. 4, 1994); PA0 U.S. Pat. No. 5,350,299 (Gallant, Sep. 27, 1994); and PA0 International (PCT) Patent Application, Publication No. WO 93/10718 (Goldsmith, published Jun. 10, 1993).
Known devices such as these suffer from one or all of the following disadvantages:
1) their delivery rates are not precisely controlled, or even controllable, so that the rates vary greatly depending on how full their reservoirs are;
2) they are prone to clogging at least one point in the delivery path;
3) they do not efficiently use enough of the available pressure of the delivered propellant gas; and
4) they are too bulky or heavy to be easily mounted near the dentist, such as on the dental tray attached to the chair.
U.S. Pat. No. 5,618,177 (Abbott, Apr. 8, 1997) overcomes many problems of earlier systems in that it delivers a smooth flow of abrasive powder into the output gas stream. However, its inability to accurately meter, rather than just ensure, proper flow, as well as its size, means that an improved system is still needed. This invention provides such improvement.
One other shortcoming of existing arrangements for providing powder under pressure to an abrasive dental tool is that they require greater pressure to drive the powder than is generally available to other pneumatic dental tools such as a drill. It would be better for the abrasion tool to be able to use existing pressure sources, since this would eliminate the need to have multiple pressure sources or retrofitted manifolds.